The respective face of the source body is optically detected with a detection device by means of the contrast between the environment of the face and the face. The slice thickness required for a predetermined slice weight is determined from the specific gravity of the source body and face. The separation of the disc-shaped body is controlled with the value determined in this way.
Many foods such as cheese, ham, sausage, etc. are provided for sale in the market prepacked in sliced form, a relatively large proportion being supplied as so-called equalized goods with a fixed weight. When cutting up the products, the fixed weight must be maintained as exactly as possible according to the tolerance standards of the prepacking regulations. Fluctuations in product cross-section within a product string, and also from one product string to the next, make it difficult, if not impossible, to meet these tolerance standards. Therefore it is advantageous to utilize methods for detecting the product cross-section at the right time, which allow adaptation of product advance the moment there is also a change in cross-section.
DE-C-28 20 583 C2 and EP 246 668 A2 describe a method in which the weight of the already cut-off slices is determined with scales, and advance is adjusted according to the measured total weight. This method is intricate and tedious because all scales need a certain time to reach their position of equilibrium. Rapid weighing is therefore thwarted by physical laws such as e.g. natural oscillation processes, poor filtering of interference, etc. and the unavoidable time lapse between weighing and cutting operations.
Also known, e.g. from U.S. Pat. No. 4,557,019, are methods which are based on scanning the surfaces of the products before the cutting operation. In this case the outer casing of the source body to be sliced is scanned, e.g. by a triangulation method, before the cutting operation and advance is later adapted during the cutting operation according to the previously calculated volume or the measured cross-sections. Due to the non-uniform shape of the products, however, the exact positioning is lost during transport to the cutting shaft. When the products are picked up by a gripper claw, particularly due to the associated buckling movement. Hence the actual cross-section is changed from the calculated one. Due to the limited number of cameras, shadow areas in which the surface is not correctly detected occur, depending on the actual shape of the products. Also, hollow layers and severe distortions as a rule lead to overestimates of volume. Although the illumination and soiling of the scanning device in this method are relatively unproblematic, the actual cross-sectional area is not determined with sufficient accuracy.
DE-A-38 08 790 A1 describes a method for detecting the cut surfaces during the cutting operation, in which the cut surface is illuminated with lamps and detected with a CCD camera, using the reflection behavior. Both the camera and the lamps are mounted in front of the cut surface. The method is limited in that if the height of fall cannot be made high enough for reasons of cutting technology, such as in the case of portions which, owing to their height increasing with cutting or special shingle techniques, come very close in front of the cutting surface. Also, problems arise with cutting devices which work with very high cutting outputs of up to 2,000 cuts per minute. At these high speeds the slice which has already been cut off is still falling while the picture is already being taken for the following slice which has not yet been cut. The camera and lighting angle must therefore inevitably be very flat, and it is almost impossible to accomplish illumination without throwing disturbing shadows or without uncontrolled back reflection. Furthermore, the camera and the lighting must be mounted in areas with extremely high contamination.
The above-mentioned drawbacks could be reduced with the cutting device described in DE-C-37 14 199 C2, by mounting the lighting elements directly behind the cutting plane adjacent to the cutting blade. Due to direct determination of the cut surface, the actual cross-sectional area can be detected very precisely. With the apparatus described, however, there arises problems with the picture quality due to reflection and shadow formation with different source bodies and due to shadow formation by additional elements of the cutting apparatus, e.g. holding arms.
U.S. Pat. No. 5,129,298 describes a cutting apparatus in which the contour of a source body is illuminated with dark field lighting. For this purpose, three lighting elements are mounted behind the source body for lighting a ground glass screen, in order to direct light rays obliquely from above in the longitudinal direction of the source body onto the upper cut edge and obliquely from the side onto the side edges. Due to reflection and shadow formation, however, the quality of illumination can be impaired. Also, hollow layers and indentations on the underside of the product cannot be detected.
From DE-C-42 06 196 C2 is known the use of an advance tunnel in conjunction with cutting machines. Traditional advance tunnels however are used only for safety reasons and for better guiding of the source body.